Marquee Lights

Here's a simple effect suitable for adding a little pizazz to title screens or
whatnot. The "lights" are nice and square and are, in fact, only a 1/2 pixel
high. Too bad that anyone who recalls the TRS-80 is likely to think the
pixels were that size. Oh well, I know there's a lot more going on
here than meets the eye.

The demo only works on a TRS-80 Model III. I might be able to make it work on
a Model I but it'd require a different approach.

Instructions

The light pixels are generated in a stream starting at the bottom left and
moving clockwise. It starts at a spacing of 6 pixels which can be tightened
up by holding the left arrow key and spread out by holding the right arrow key.
Hold ENTER to suspend light production. Hold space bar to add lights.

It only checks if a key is held so a light touch is needed on the left and
right arrow keys.